Implantable neurostimulator devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder subluxation, etc.
FIGS. 1A and 1B shows a traditional Implantable Pulse Generator (IPG) 100, which includes a biocompatible device case 30 formed of a conductive material such as titanium for example. The case 30 typically holds the circuitry and a battery necessary for the IPG 100 to function, although IPGs can also be powered via external RF energy and without a battery. The IPG 100 includes in this simple example an electrode array 102 containing a linear arrangement of electrodes 106. The electrodes 106 are carried on a flexible body 108, which also houses the individual electrode leads 112 coupled to each electrode. In the illustrated embodiment, there are eight electrodes on array 102, labeled E1-E8, although the number of electrodes is application specific and therefore can vary. Array 102 couples to case 30 using a lead connector 38, which is fixed in a non-conductive header material 36 such as epoxy for example. As is well known, the array 102 is implanted in an appropriate location in a patient to provide suitable simulative therapy, and is coupled through the patient's tissue to the IPG 100, which may be implanted somewhat distant from the location of the array.
As shown in FIG. 1B, the IPG 100 typically includes an electronic substrate assembly 14 including a printed circuit board (PCB) 16, along with various electronic components 20, such as microprocessors, integrated circuits, and capacitors mounted to the PCB 16. Two coils (more generally, antennas) are generally present in the IPG 100: a telemetry coil 13 used to transcutaneously transmit/receive data to/from an external controller (not shown); and a charging coil 18 for transcutaneously charging or recharging the IPG's battery 26 using an external charger (also not shown).
A portion of circuitry 20 in the IPG 100 is dedicated to the provision of therapeutic currents to the electrodes 106. Such currents are typically provided by current sources 150, as shown in FIGS. 2A and 2B. In many current-source based architectures, some number of current sources 150 are associated with a particular number of electrodes 106. For example, in FIG. 2A, it is seen that N electrodes E1-EN are supported by N dedicated current sources 1501-150N. In this example, and as is known, the current sources 150 are programmable (programming signals not shown) to provide a current of a certain magnitude and polarity to provide a particular therapeutic current to the patient. For example, if source 1502 is programmed to source a 5 mA current, and source 1503 is programmed to sink a 5 mA current, then 5 mA of current would flow from anode E2 to cathode E3 through the patient's tissue, R, hopefully with good therapeutic effect. Typically such current is allowed to flow for a duration, thus defining a current pulse, and such current pulses are typically applied to the patient with a given frequency. If the therapeutic effect is not good for the patient, the electrodes chosen for stimulation, the magnitude of the current they provide, their polarities, their durations, or their frequencies could be changed.
(FIG. 2A shows that each of the electrodes is tied to a decoupling capacitor. As is well known, decoupling capacitors promote safety by prevent the direct injection of current form the IPG 100 into the patient. For simplicity, decoupling capacitors are not shown in subsequent drawings, even though they are typically present in practical implementations).
FIG. 2B shows another example current source architecture using a switch matrix 160. In this architecture, the switch matrix 160 is used to route current from any of the sources 150P to any of the electrodes EN. For example, if source 1052 is programmed to source a 5 mA current, and source 1051 is programmed to sink a 5 mA current, and if source 1502 is coupled to electrode E2 by the switch matrix 160, and if source 1501 is connected to electrode E3 by the switch matrix 160, then 5 mA of current would flow from anode E2 to cathode E3 through the patient's tissue, R. In this example, because any of the current sources 150 can be connected to any of the electrodes, it is not strictly required that the number of electrodes (N) and the number of current sources (P) be the same. In fact, because it would perhaps be rare to activate all N electrodes at once, it may be sensible to make P less than N, to reduce the number of sources 150 in the IPG architecture. This however may not be the case, and the number of sources and electrodes could be equal (P=N). Although not shown, it should be understood that switch matrix 160 would contains P×N switches, and as many control signals (C1,1-CP,N), to controllably interconnect all of the sources 150P to any of the N electrodes. Further details of a suitable switch matrix can be found in U.S. Patent Pub. U.S. Patent Publication 2007/0038250, which is incorporated herein by reference.
The architecture of FIG. 2B, like the architecture of FIG. 2A, also comprises some number of current sources 150 (P) associated with a particular number of electrodes 106 (N). Other more complicated current architectures exist in the implantable stimulator art. See, e.g., the above-incorporated '250 Publication. But again generally such approaches all require some number of current sources 150 to be associated with a particular number of electrodes 106.
The inventor considers the association of numbers of current sources and electrodes to be limiting because such architectures do not easily lend themselves to scaling. As implantable stimulator systems become more complicated, greater numbers of electrodes will provide patients more flexible therapeutic options. However, as the number of electrodes grows, so too must the number of current sources according to traditional approaches discussed above. This is considered undesirable by the inventor, because current source circuitry—even when embodied on an integrated circuit—is relatively large and complicated. Newer architectural approaches are thus believed necessary by the inventor to enable the growth of more complicated implantable stimulator systems, and such new architectures are presented herein.